In operation of machinery and other plant it is important to ensure the cleanliness and integrity of lubricating oils used. Lubricating oils can often be contaminated by water or moisture. Oil can also be contaminated by other substances or materials such as microscopic wear debris or contaminated by other liquids. Contamination of oil results in loss of lubrication integrity and can result in excessive wear of machinery and plant.
Different types of equipment are known for use in separation of solids from liquids. Centrifuges are a common form of device which can be used for this purpose and are of two general types, namely sedimentation centrifuges, which require a difference between the densities of the two or more phases to be separated; and centrifugal filters, in which the solid phase is supported and retained on a permeable membrane through which the liquid phase is free to pass. Self-powered centrifugal fluid cleaning devices are also known for cleaning lubricating fluids of solid contaminants in engines and like mechanisms. Notwithstanding the simplicity and efficiency with which such devices separate solids from the fluid passing therethrough, there are a number of limitations attached to their usage which have hither-to served to limit their widespread use.
Some centrifuges have draining limitations which can be reduced by exposing the centrifuge housing to an above-ambient pressure possibly from an engine crank case, although this then requires either a corresponding increase in supply pressure to maintain the pressure drop across the centrifuge rotor nozzles, acceptance of a reduced rotation efficiency, or by using a suction pump driven by way of a power take off from the engine or machine being lubricated by the circulated fluid. Another method proposed in the past to overcome the draining limitations of such centrifuges is to provide a cleaner in which a proportion of a circulated fluid is diverted with a drainage assistance arrangement including a venturi arrangement through which the non-diverted fluid is passed. The venturi develops a significant pressure drop in a region into which opens an induction port connected to the cleaner sump so that the cleaned fluid can be entrained into the non-diverted fluid and returned to circulation.
These arrangements have not been particularly effective in removal of the fluid from the base of the rotor. A failure to accomplish this effectively leads to the fluid “backing up” or accumulating in the base and this affects the rotor speed and therefore separation efficiency.
Devices and systems that have been used to remove water contamination include settling tanks or reservoirs, centrifuges, water absorbing filters, and vacuum dehydration oil purifiers. All these devices have significant limitations in either their water removal capabilities, ease of operation, capital costs, or operating costs. Some of these devices are ineffective in separating oil-water emulsions and are not capable of removing dissolved water. Centrifuges are effective in removing free water from the oil but are expensive and have limited capability in separating oil-water emulsions. Water absorbing filters are effective in removing free water but have a marginal effect in removing emulsified or dissolved water from the oil. In addition, water-absorbing filters have a limited capacity for water and are typically only used in applications where trace amounts of water are present.
Several types of vacuum dehydration oil purifiers have been used for oil dehydration. These generally operate under the principle of vacuum distillation, mass transfer of moisture from the oil to dry air, or a combination of the two. While vacuum distillation and mass transfer systems do remove free, emulsified and dissolved water, they have several drawbacks that have prevented their widespread use.
Vacuum purifiers are also subject to foaming within the vessels as water is vaporized within the oil. This foam has a lower specific gravity than the oil and can cause malfunctioning controls and a reduction in the performance of the purifier. Due to their ability to remove free, emulsified or dissolved water from oil, vacuum dehydration oil purifiers have become the desired method for water removal from oil. The drawbacks associated with vacuum oil purifiers have prohibited these purifiers from being widely used and/or the purifiers are not practical on the majority of lubrication or hydraulic systems. Because of their relatively large size and costs, they are limited to non-mobile, stationary applications, and are not practical for use on mobile equipment. Further due to their high capital cost, they are typically not permanently installed in a system unless it is a relatively large, expensive lubrication or hydraulic system. Instead, they are usually shared by several systems by using one to purify the oil on one machine or reservoir for a period of time, and then by moving it to another machine, etc. When the purifier is being used in this manner, the oil in the machines that are not connected to the purifier can become contaminated with water. This oil will remain contaminated until the purifier can be reattached to them and the oil dehydrated again.
Membrane based systems have been used to remove water from organic systems. It must, however, be recognized that the presence of either pores or defects in a membrane used for this purpose will result in the hydraulic permeation of the oil to the permeate side. This situation will result in the loss of oil. It will also allow the non-volatile oil to coat the permeate side of the membrane, thereby fouling the membrane and reducing its effectiveness in permeating water.